This invention relates generally to radio frequency antennas and more particularly to reflector type radio frequency antennas.
As is known in the art in many applications, it is sometimes necessary to provide compact radio frequency antennas having extremely low side lobe characteristics. One type of compact antenna is a reflector antenna wherein energy coupled to the feed of the antenna is reflected by a reflective surface prior to radiation into free space. One well known method for obtaining low side lobes from a reflector antenna is to shape the pattern of the fed energy so that the amplitude of such fed energy is greatly reduced at the edge of the reflector. That is, the fed energy is reduced at the edge of the reflector so that the edge will not scatter the energy incident thereon and thereby generate unwanted side lobes in the free-space radiation pattern.
Various techniques have been used to taper the energy of the fed energy and thereby reduce the amount of the fed energy striking the edge of the reflector; for example, scalar reflector fed antennas, such as: corrugated, dielectric or multi-mode feed type antennas; and multi-element array fed type antennas. While such antennas do provide a degree of illumination taper, they have a relative large height profile and are therefore not compact enough for many applications, such as airborne applications.